1254:
97:. The strings should be three characters long or more for the examination to be successful. Then, the distances between consecutive occurrences of the strings are likely to be multiples of the length of the keyword. Thus finding more repeated strings narrows down the possible lengths of the keyword, since we can take the
223:
each of these numbers. If any number is repeated in the majority of these factorings, it is likely to be the length of the keyword. This is because repeated groups are more likely to occur when the same letters are encrypted using the same key letters than by mere coincidence; this is especially true
196:
The difficulty of using the
Kasiski examination lies in finding repeated strings. This is a very hard task to perform manually, but computers can make it much easier. However, care is still required, since some repeated strings may just be coincidence, so that some of the repeat distances are
262:
Kasiski actually used "superimposition" to solve the Vigenère cipher. He started by finding the key length, as above. Then he took multiple copies of the message and laid them one-above-another, each one shifted left by the length of the key. Kasiski then observed that each
284:
The analyst shifts the bottom message one letter to the left, then one more letters to the left, etc., each time going through the entire message and counting the number of times the same letter appears in the top and bottom
108:, and the distance between corresponding characters is a multiple of the keyword length, the keyword letters will line up in the same way with both occurrences of the string. For example, consider the plaintext:
224:
for long matching strings. The key letters are repeated at multiples of the key length, so most of the distances found in step 1 are likely to be multiples of the key length. A common factor is usually evident.
250:
Using the solved message, the analyst can quickly determine what the keyword was. Or, in the process of solving the pieces, the analyst might use guesses about the keyword to assist in breaking the message.
288:
The number of "coincidences" goes up sharply when the bottom message is shifted by a multiple of the key length, because then the adjacent letters are in the same language using the same alphabet.
67:, the Kasiski examination allows a cryptanalyst to deduce the length of the keyword. Once the length of the keyword is discovered, the cryptanalyst lines up the ciphertext in
197:
misleading. The cryptanalyst has to rule out the coincidences to find the correct length. Then, of course, the monoalphabetic ciphertexts that result must be cryptanalyzed.
201:
A cryptanalyst looks for repeated groups of letters and counts the number of letters between the beginning of each repeated group. For instance, if the ciphertext were
1234:
1064:
476:
267:
was made up of letters encrypted with a single alphabet. His method was equivalent to the one described above, but is perhaps easier to picture.
155:". The two instances will encrypt to different ciphertexts and the Kasiski examination will reveal nothing. However, with a 5-character keyword "
902:
118:" is a repeated string, and the distance between the occurrences is 20 characters. If we line up the plaintext with a 6-character keyword "
274:. Instead of looking for repeating groups, a modern analyst would take two copies of the message and lay one above another.
469:
270:
Modern attacks on polyalphabetic ciphers are essentially identical to that described above, with the one improvement of
76:
277:
Modern analysts use computers, but this description illustrates the principle that the computer algorithms implement.
227:
Once the keyword length is known, the following observation of
Babbage and Kasiski comes into play. If the keyword is
895:
409:
692:
333:
682:
462:
687:
253:
Once the interceptor knows the keyword, that knowledge can be used to read other messages that use the same key.
1285:
1113:
1044:
888:
271:
1229:
1184:
987:
702:
243:"messages", each encrypted using a one-alphabet substitution, and each piece can then be attacked using
188:". The two instances will encrypt to the same ciphertext and the Kasiski examination will be effective.
1108:
311:
1224:
1214:
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424:
1209:
1199:
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945:
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Kasiski, F. W. 1863. Die
Geheimschriften und die Dechiffrir-Kunst. Berlin: E. S. Mittler und Sohn
98:
997:
940:
90:
machine has been used, this method may allow the deduction of the length of individual rotors.
356:
1257:
1103:
1049:
813:
504:
220:
36:
738:
93:
The
Kasiski examination involves looking for strings of characters that are repeated in the
1219:
1143:
844:
748:
674:
8:
972:
858:
772:
606:
235:
th letter must have been enciphered using the same letter of the keytext. Grouping every
60:
1088:
1072:
1014:
839:
758:
664:
596:
292:
244:
80:
527:
387:
Franksen, O. I. 1985 Mr. Babbage's Secret: the Tale of a Cipher—and APL. Prentice Hall
40:
1148:
1138:
1004:
808:
728:
697:
591:
522:
405:
314:- A video that shows how to break a Vigenère ciphertext using the Kasiski examination
75:
is the length of the keyword. Then each column can be treated as the ciphertext of a
44:
216:
groups is 10. The analyst records the distances for all repeated groups in the text.
1083:
935:
485:
629:
586:
555:
537:
48:
402:
The Code Book: The
Science of Secrecy from Ancient Egypt to Quantum Cryptography
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64:
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1194:
1153:
1133:
1024:
982:
957:
800:
654:
634:
614:
565:
545:
291:
Having found the key length, cryptanalysis proceeds as described above using
87:
84:
20:
1189:
1029:
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967:
911:
733:
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550:
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649:
397:
1128:
1098:
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1054:
852:
834:
639:
570:
94:
104:
The reason this test works is that if a repeated string occurs in the
1118:
790:
105:
1163:
1123:
560:
307:
Cryptanalysis: Breaking a Vigenère ciphertext with
Kasiski's test
1039:
753:
619:
493:
723:
718:
659:
63:
where the substitution alphabets are chosen by the use of a
47:
in 1863, but seems to have been independently discovered by
1065:
Cryptographically secure pseudorandom number generator
446:
1277:
896:
470:
358:Historical Cryptography: The Vigenere Cipher
79:. As such, each column can be attacked with
331:
903:
889:
484:
477:
463:
151:" and the second instance lines up with "
191:
361:, Trinity College Hartford, Connecticut
1278:
354:
884:
458:
404:, London: Fourth Estate, p. 78,
396:
239:th letter together, the analyst has
429:, Michigan Technological University
335:Kasiski Analysis: Breaking the Code
37:polyalphabetic substitution ciphers
13:
257:
111:crypto is short for cryptography.
77:monoalphabetic substitution cipher
14:
1297:
299:
1253:
1252:
910:
122:" (6 does not divide into 20):
54:
1114:Information-theoretic security
417:
390:
381:
372:
348:
325:
1:
318:
43:. It was first published by
7:
1230:Message authentication code
1185:Cryptographic hash function
988:Cryptographic hash function
35:) is a method of attacking
10:
1302:
1109:Harvest now, decrypt later
1248:
1225:Post-quantum cryptography
1177:
918:
880:
827:
799:
771:
711:
673:
605:
579:
536:
503:
492:
454:
450:
332:Rodriguez-Clark, Daniel,
231:letters long, then every
1215:Quantum key distribution
1205:Authenticated encryption
1060:Random number generation
355:R. Morelli, R. Morelli,
280:The generalized method:
1210:Public-key cryptography
1200:Symmetric-key algorithm
993:Key derivation function
953:Cryptographic primitive
946:Authentication protocol
931:Outline of cryptography
926:History of cryptography
212:, the distance between
159:" (5 divides into 20):
143:the first instance of "
99:greatest common divisor
16:Method in cryptanalysis
998:Secure Hash Algorithms
941:Cryptographic protocol
486:Classical cryptography
101:of all the distances.
1286:Cryptographic attacks
1104:End-to-end encryption
1050:Cryptojacking malware
192:A string-based attack
180:both occurrences of "
83:. Similarly, where a
1220:Quantum cryptography
1144:Trusted timestamping
845:Index of coincidence
749:Reservehandverfahren
272:coincidence counting
61:substitution ciphers
973:Cryptographic nonce
864:Kasiski examination
859:Information leakage
25:Kasiski examination
1089:Subliminal channel
1073:Pseudorandom noise
1015:Key (cryptography)
840:Frequency analysis
739:RasterschlĂĽssel 44
293:frequency analysis
245:frequency analysis
81:frequency analysis
59:In polyalphabetic
51:as early as 1846.
1270:
1269:
1266:
1265:
1149:Key-based routing
1139:Trapdoor function
1005:Digital signature
876:
875:
872:
871:
767:
766:
219:The analyst next
147:" lines up with "
45:Friedrich Kasiski
1293:
1256:
1255:
1084:Insecure channel
936:Classical cipher
905:
898:
891:
882:
881:
501:
500:
479:
472:
465:
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451:
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426:Kasiski's Method
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184:" line up with "
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158:
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121:
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33:Kasiski's method
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1300:
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1173:
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909:
868:
823:
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538:Polybius square
532:
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258:Superimposition
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185:
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156:
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144:
141:
119:
115:
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71:columns, where
57:
49:Charles Babbage
41:Vigenère cipher
27:(also known as
17:
12:
11:
5:
1299:
1289:
1288:
1268:
1267:
1264:
1263:
1261:
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1249:
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1237:
1235:Random numbers
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1202:
1197:
1192:
1187:
1181:
1179:
1175:
1174:
1172:
1171:
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1161:
1159:Garlic routing
1156:
1151:
1146:
1141:
1136:
1131:
1126:
1121:
1116:
1111:
1106:
1101:
1096:
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1079:Secure channel
1076:
1070:
1069:
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1057:
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1047:
1042:
1037:
1035:Key stretching
1032:
1027:
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1007:
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978:Cryptovirology
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963:Cryptocurrency
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744:Reihenschieber
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505:Polyalphabetic
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371:
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300:External links
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165:bcdeabcdeabcde
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128:abcdefabcdefab
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39:, such as the
29:Kasiski's test
15:
9:
6:
4:
3:
2:
1298:
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1240:Steganography
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1195:Stream cipher
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1154:Onion routing
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1147:
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1135:
1134:Shared secret
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1025:Key generator
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983:Hash function
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958:Cryptanalysis
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828:Cryptanalysis
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801:Steganography
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675:Transposition
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411:1-85702-879-1
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173:is short for
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136:is short for
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127:
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109:
107:
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96:
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88:stream cipher
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82:
78:
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66:
62:
52:
50:
46:
42:
38:
34:
30:
26:
22:
21:cryptanalysis
1272:
1190:Block cipher
1030:Key schedule
1020:Key exchange
1010:Kleptography
968:Cryptosystem
912:Cryptography
863:
734:One-time pad
607:Substitution
443:
431:, retrieved
425:
419:
401:
398:Singh, Simon
392:
383:
374:
363:, retrieved
357:
350:
339:, retrieved
334:
327:
279:
276:
269:
264:
261:
207:
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179:
174:
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125:
113:
103:
92:
72:
68:
58:
55:How it works
32:
28:
24:
18:
1178:Mathematics
1169:Mix network
786:Code talker
665:Running key
597:Four-square
341:30 November
1129:Ciphertext
1099:Decryption
1094:Encryption
1055:Ransomware
835:Cryptogram
729:Kama Sutra
698:Rail fence
693:Myszkowski
640:Chaocipher
592:Two-square
571:VIC cipher
523:Trithemius
319:References
95:ciphertext
1119:Plaintext
759:Solitaire
497:by family
106:plaintext
1280:Category
1258:Category
1164:Kademlia
1124:Codetext
1067:(CSPRNG)
1045:Machines
847:(Units:
683:Columnar
630:Beaufort
587:Playfair
561:Tap code
556:Nihilist
528:Vigenère
400:(1999),
285:message.
177:graphy.
169:bcdeabc
140:graphy.
132:cdefabc
919:General
625:Autokey
513:Alberti
494:Ciphers
312:YouTube
221:factors
206:THJAQWN
65:keyword
1040:Keygen
814:Grille
754:Slidex
688:Double
655:Pigpen
635:Caesar
620:Atbash
615:Affine
580:Square
566:Trifid
546:ADFGVX
518:Enigma
433:1 June
408:
365:4 June
265:column
186:abcdea
182:crypto
175:crypto
171:crypto
167:abcdea
163:abcdea
153:cdefab
149:abcdef
145:crypto
138:crypto
134:crypto
130:cdefab
126:abcdef
120:abcdef
116:crypto
1075:(PRN)
809:Bacon
773:Codes
724:DRYAD
719:BATCO
712:Other
703:Route
660:ROT13
645:Great
551:Bifid
157:abcde
85:rotor
851:and
819:Null
791:Poem
781:Book
650:Hill
435:2015
406:ISBN
367:2015
343:2014
853:Nat
849:Ban
310:on
214:FGX
208:FGX
204:FGX
31:or
19:In
1282::
23:,
904:e
897:t
890:v
855:)
478:e
471:t
464:v
295:.
247:.
241:N
237:N
233:N
229:N
210:Q
114:"
73:n
69:n
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